[web] Fix url updates when using Router (#24798)

lib/web_ui/lib/src/engine/window.dart

@@ -44,13 +44,17 @@ class EngineFlutterWindow extends ui.SingletonFlutterWindow {
   /// button, etc.
   @visibleForTesting
   BrowserHistory get browserHistory {
+    return _browserHistory ??=
+        MultiEntriesBrowserHistory(urlStrategy: _urlStrategyForInitialization);
+  }
+
+  UrlStrategy? get _urlStrategyForInitialization {
     final UrlStrategy? urlStrategy = _isUrlStrategySet
         ? _customUrlStrategy
         : _createDefaultUrlStrategy();
     // Prevent any further customization of URL strategy.
     _isUrlStrategySet = true;
-    return _browserHistory ??=
-        MultiEntriesBrowserHistory(urlStrategy: urlStrategy);
+    return urlStrategy;
   }
 
   BrowserHistory? _browserHistory;
@@ -59,8 +63,14 @@ class EngineFlutterWindow extends ui.SingletonFlutterWindow {
     if (_browserHistory is SingleEntryBrowserHistory) {
       return;
     }
-    final UrlStrategy? strategy = _browserHistory?.urlStrategy;
-    await _browserHistory?.tearDown();
+
+    final UrlStrategy? strategy;
+    if (_browserHistory == null) {
+      strategy = _urlStrategyForInitialization;
+    } else {
+      strategy = _browserHistory?.urlStrategy;
+      await _browserHistory?.tearDown();
+    }
     _browserHistory = SingleEntryBrowserHistory(urlStrategy: strategy);
   }
 
@@ -68,8 +78,14 @@ class EngineFlutterWindow extends ui.SingletonFlutterWindow {
     if (_browserHistory is MultiEntriesBrowserHistory) {
       return;
     }
-    final UrlStrategy? strategy = _browserHistory?.urlStrategy;
-    await _browserHistory?.tearDown();
+
+    final UrlStrategy? strategy;
+    if (_browserHistory == null) {
+      strategy = _urlStrategyForInitialization;
+    } else {
+      strategy = _browserHistory?.urlStrategy;
+      await _browserHistory?.tearDown();
+    }
     _browserHistory = MultiEntriesBrowserHistory(urlStrategy: strategy);
   }
 
@@ -261,7 +277,7 @@ external set _jsSetUrlStrategy(_JsSetUrlStrategy? newJsSetUrlStrategy);
 
 UrlStrategy? _createDefaultUrlStrategy() {
   return ui.debugEmulateFlutterTesterEnvironment
-      ? null
+      ? TestUrlStrategy.fromEntry(TestHistoryEntry('default', null, '/default'))
       : const HashUrlStrategy();
 }
 

lib/web_ui/test/window_test.dart

@@ -128,6 +128,51 @@ void testMain() {
     expect(window.browserHistory.urlStrategy.getPath(), '/baz');
   });
 
+  test('initialize browser history with default url strategy (single)', () async {
+    // On purpose, we don't initialize history on the window. We want to let the
+    // window to self-initialize when it receives a navigation message.
+
+    Completer<void> callback = Completer<void>();
+    window.sendPlatformMessage(
+      'flutter/navigation',
+      JSONMethodCodec().encodeMethodCall(MethodCall(
+        'routeUpdated',
+        <String, dynamic>{'routeName': '/bar'},
+      )),
+      (_) { callback.complete(); },
+    );
+    await callback.future;
+    expect(window.browserHistory is SingleEntryBrowserHistory, true);
+    // The url strategy should've been set to the default, and the path
+    // should've been correctly set to "/bar".
+    expect(window.browserHistory.urlStrategy, isNot(isNull));
+    expect(window.browserHistory.urlStrategy.getPath(), '/bar');
+  }, skip: browserEngine == BrowserEngine.webkit); // https://github.com/flutter/flutter/issues/50836
+
+  test('initialize browser history with default url strategy (multiple)', () async {
+    // On purpose, we don't initialize history on the window. We want to let the
+    // window to self-initialize when it receives a navigation message.
+
+    Completer<void> callback = Completer<void>();
+    window.sendPlatformMessage(
+      'flutter/navigation',
+      JSONMethodCodec().encodeMethodCall(MethodCall(
+        'routeInformationUpdated',
+        <String, dynamic>{
+          'location': '/baz',
+          'state': null,
+        },
+      )),
+      (_) { callback.complete(); },
+    );
+    await callback.future;
+    expect(window.browserHistory is MultiEntriesBrowserHistory, true);
+    // The url strategy should've been set to the default, and the path
+    // should've been correctly set to "/baz".
+    expect(window.browserHistory.urlStrategy, isNot(isNull));
+    expect(window.browserHistory.urlStrategy.getPath(), '/baz');
+  }, skip: browserEngine == BrowserEngine.webkit); // https://github.com/flutter/flutter/issues/50836
+
   test('can disable location strategy', () async {
     // Disable URL strategy.
     expect(() => jsSetUrlStrategy(null), returnsNormally);